WIZnet Developer Forum

Spurious Retransmission

Hello,

I have a project involving a W5500 chip. I have a using a few sockets, all TCP.

The problem I have is with the one implementing a web server. If the network is slow, but not always necessary, it is impossible to open the web page. Adding breakpoints, the code to deal with socket data is not even hit.

Wireshark shows packets as below:

61247 0.653357000 192.168.1.9 192.168.1.123 TCP 66 80 13 61247→80 [SYN] Seq=0 Win=8192 Len=0 MSS=1260 WS=4 SACK_PERM=1
80 0.653703000 192.168.1.123 192.168.1.9 TCP 60 61247 14 80→61247 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0
61247 1.153147000 192.168.1.9 192.168.1.123 TCP 66 80 46 [TCP Spurious Retransmission] 61247→80 [SYN] Seq=0 Win=8192 Len=0 MSS=1260 WS=4 SACK_PERM=1
80 1.153498000 192.168.1.123 192.168.1.9 TCP 60 61247 47 80→61247 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0
61247 1.653172000 192.168.1.9 192.168.1.123 TCP 62 80 108 [TCP Spurious Retransmission] 61247→80 [SYN] Seq=0 Win=8192 Len=0 MSS=1260 SACK_PERM=1
80 1.653555000 192.168.1.123 192.168.1.9 TCP 60 61247 109 80→61247 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0

.9 is my computer and .123 device with the W5500 chip.

Why would it reset but acknowledge the SYN packet?

Thanks.

Hello, cio74

It looks you use W5500 as server and the server send RST+ACK to client

There are many reasons why server send RST+ACK and It is hard to know with only wireshark.

So, before all, I would like to check something more.

  1. I do not get your mention. You mean when only network is slow, can not open web page right ?

  2. So, in normal network condition( means does not slow), web page opened ?

  3. When client send SYN, is server(W5500) in Listen statue ?

Thank you,

Lawrence

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